Written evidence submitted by the Dipterists Forum (INS0030)

1.0              Sources of information about the Dipterists Forum and its Recording Schemes

Dipterists Forum is an umbrella organisation for all UK Diptera recording schemes. It has a website: https://dipterists.org.uk/home and a Facebook page: https://www.facebook.com/groups/DipteristsForum/

The forum publishes a biannual, peer reviewed journal: Dipterists Digest, inaugurated in 1988. Our biannual Bulletin provides detail of forthcoming meetings and news from individual Recording Schemes.

There are currently 28 recording schemes and study groups. A list, including contact details, and URLs appears on the back cover of each edition of the Bulletin.

The Hoverfly Recording Scheme for Great Britain (HRS) is most relevant to this inquiry. It has its own website: http://hoverfly.uk/hrs/ and a Facebook page https://www.facebook.com/groups/609272232450940.

Several other Diptera Recording Schemes have their own Facebook page and a few, such as the Tachinidae Recording Scheme (https://tachinidae.org.uk/blog/), have websites.

2.0              Evidence

2.1              The current evidence base for insect abundance in the UK

There are almost no British “gold standard” datasets, ideally suited to looking at long-term trends in abundance and diversity in UK insects. Such datasets are collected in a structured and systematic fashion over a long timescale, providing robust data on the fate of British insects. The main exceptions involve moths and butterflies, but there is also a long-term dataset for aerial aphids. In the absence of such data, it is necessary to access ad-hoc data mainly assembled by ‘amateur’ natural historians via ‘Recording Scheme’ that are co-ordinated by the Biological Records Centre at UKCEH. These schemes cover a multitude of insect taxa, amongst which the Diptera schemes are very active. Unfortunately, the numbers of competent taxonomic specialists in the ’amateur’ community are small and consequently datasets for many of the most challenging but potentially important families are extremely limited. In the case of flies, this deficiency is especially notable amongst the higher flies where families such as the Anthomyiidae may prove to be very significant pollinators.

2.1.1              Datasets from national recording schemes

There is a well-established system that facilitates a data flow from recording schemes to the Biological Records Centre and on to the National Biodiversity Network (NBN), and the Global Biodiversity Information Facility (GBIF). Scientists world-wide can access these data. A GBIF search for the Dipterists forum reveals 19 datasets, which have been cited in 86 research studies. Societies such as Dipterists Forum clearly play a significant role in the understanding of UK insect ecology and abundance.

2.1.2              Data from the Hoverfly recording scheme (HRS).

Hoverflies (the family Syrphidae) are our most prominent Diptera ‘pollinators’. This Recording Scheme has been ongoing since 1976 (see Appendix 1) and is extremely active. It engages with a huge number of observers and receives records from several thousand people each year. However, of that body of observers, a tiny fraction is responsible for the majority of the data (~75 people generate 50% of the data each year). This dataset is by far the most powerful of the ‘pollinator’ datasets (currently 1.73 million records) but it has several important limitations (see section 2.1.4).

In the absence of “gold standard” data, statistical methods have been developed over the last couple of decades which attempt to extract trends from ad-hoc data, by correcting for the inherent biases. Stuart Ball has been amongst the leading proponents of this approach and has provided the following analysis. Notwithstanding known biases in the data, the following analysis points to a substantial and ongoing process of decline in which over 50% of species for which there are sufficient data to model (227 species or ~80% of British species).

2.1.3              Trends in relative frequency of Britain’s hoverflies

Data from recording schemes is often described as “presence only” data, as it does not usually include information about the abundance of species [1]. Therefore, statistical analysis is largely confined to estimates of the relative frequency of recording. The following analysis is generated by FRESCALO (FREquency SCAling LOcal), a methodology developed by Mark Hill [2], formerly head of BRC. The methodology used is summarised as follows:

• FRESCALO analysis uses unique combinations of location (in this case, 10x10km squares of OSGB grid) species and year – roughly 0.5M unique combinations.
• Result is a “TFactor” for each species and year – a summary of the relative frequency of a species corrected for local recording effort – the recording in a “neighbourhood” of around 50 squares that are both close to and environmentally similar (in terms of topography, land cover and climate) to the target square.
• For each species with sufficient data (i.e., records in at least 2/3 of the years – 227 species in this case), do a Spearman Rank correlation between TFactor and year. If the slope is sig. different from zero (p<=0.05) then the species is categorised as “Decreasing” if the slope is ‑ve and “Increasing” if it is +ve, otherwise “No change”. The right-hand plot shows the numbers of species falling in these categories.
• Fit a smoothing spline (5 df) between TFactor and year and predict value for each year. Express each year’s predicted value as a percentage of the value for a base year (in this case 1980). That gives an “index” on the same scale for each species and year.
• Calculate the geometric mean of the index values across species for each year (and generate a confidence interval using bootstrapping). This is the left-hand plot. This index score method is based on that used by the Breeding Bird Survey and Butterfly Monitoring Scheme for things like their woodland or farmland bird index.

2.1.4              Limitations of the HRS dataset

The nature of records contributing to HRS has changed (radically!) over the last decade – especially since the establishment of the UK Hoverflies Facebook group. Over half the records now come from photos posted online. This has biased the data towards obvious and photogenic species, compared to the more obscure and cryptic species, some of which are not even perceived to be hoverflies (“little black jobs” like Pipizines, Platycheirus, etc.). IF these obvious and photogenic species have a preponderance of increasing species, and the obscure ones are more often amongst the declining ones, then this will exaggerate the declines. The HRS team have published analyses showing some evidence this is true[3].

2.2              Gaps in the current evidence base, and scientific understanding, that require further research.

The current evidence-base for Diptera depends upon a tiny number of skilled specialists to make sure that (as far as possible) the species’ identifications are accurate. Stuart Ball and Roger Morris provide oversight of that process for hoverflies, including disseminating the results of the scheme. They have published a wide variety of analyses, mainly in Dipterists Digest and in the Proceedings and Transactions of the British Entomological and Natural History Society. Both these journals lack a journal impact factor from Clarivate Analytics and do not feature in the citation indexes that generate the data for research discovery tools like Clarivate’s Web of Science (see section 2.7.1 for discussion of the impact of this). The increasing shift towards pay to publish (APCs) rather than pay to read platforms means that amateurs, with a great deal of knowledge, and who are engaged in producing relevant analyses[4] [5] [6] [7] [8] tend more and more to publish in these smaller free to publish journals. This problem is not confined to the HRS but is felt most acutely by its organisers. Similar problems pertain to other British ‘amateur’ specialists and will also be felt in less developed nations where funding is very restricted.

Despite problems with publishing results, the HRS has developed a body of evidence that points to climate change and especially drought and soil moisture deficit[9] as a likely modern driver of Diptera decline that potentially extends well beyond Diptera into the ongoing declines of a wide range of breeding birds[10] and potentially, also mammals such as hedgehogs and dormice that rely wholly or in part upon invertebrates as prey items. However, the connection between climate change and the declines in insects (and especially Diptera) is very difficult to prove for several reasons:

• There are no structured data that can be used to evaluate the impact of individual extreme weather events.
• Remarkably little research has been conducted into the effects of drought upon soil faunas.
• Very little is known about the relationship between changes in humidity in temperate ecosystems and insect assemblages.
• Data that do exist become increasingly thin at a regional level, making it very challenging to investigate relationships between critical weather parameters such as levels of rainfall during summer months, or periods of drought.
• There has been a tendency to evaluate climate at an averaged level such as yearly rainfall rather than investigating relationships between the duration of extreme heat and extended soil moisture deficit.

In addition, we are aware of a variety of pollinator projects whose data has not reached recording schemes. Similarly, we have encountered forest research whose datasets appear not to have entered the national dataset. Indeed, we were recently contacted by somebody who had inherited a Diptera collection that had been compiled in the pursuit of a PhD that was completely un-labelled and had been consigned to the skip by its originator. Much more effort needs to go into preservation of these data.

2.3              The effects of pesticides, such as neonicotinoids or other agricultural control methods on insects including pollinators and their impact on UK food security.

This is a subject area in which we have very limited expertise. There is an extensive literature that will doubtless be presented in other submissions.

2.4              The extent that biodiversity initiatives, such as creating reservoir populations, are addressing insect decline and whether there is sufficient coordination with the UK food system.

All biodiversity initiatives will have some benefit, but we have yet to see any specific benefit in the case of most Diptera. One exception involves re-wetting upland blanket bog[11], which demonstrates that reversing drainage has a profound and rapid effect on cranefly abundance, with corresponding benefits to uplands breeding birds.

It is noticeable, however, that despite innumerable initiatives over the past 30 years, critical wildlife assets continue along a consistent downward trajectory, suggesting that no initiative to date has been effective in even slowing declines.

Diptera may help to provide a key to this conundrum: not only are they a major food source for vertebrates, they also perform a very wide range of ecosystem functions. They are, inter-alia, pollinators, saprophages, filter-feeders, parasites and predators, all of which are responsible for regulating aspects of ecosystem function both within the soil and above ground. The role of pollinators has received much recognition and publicity, but it is likely that the most significant ecosystem function performed by Diptera involves their larvae breaking down organic matter and returning nutrients into the soil. They form a significant part of the fauna in rotting vegetable matter, leaf litter, dead wood, carrion, etc. Their critical weakness is that these larvae are largely thin-skinned, confined to living in wet or damp micro-habitats and highly susceptible to desiccation. Thus, in terms of understanding landscape modification measures that might effectively address insect decline, it is important to focus on water availability.

It is our impression that there is an ongoing tension between food production and the critical drivers of insect decline. For example, across East Anglia there is a plethora of ghost ponds; former farm ponds that have been infilled but whose presence can still be detected in the landscape[12]. That situation probably obtains elsewhere. Similarly, low-lying alluvial valleys have been drained, rivers have been straightened and floodplains built upon. These factors have all contributed to the decline in insect abundance and continue almost unabated. Re-wilding presents opportunities there is significant resistance from parts of society who regard it as a threat to food production. More effort needs to go into creating a common understanding of the role wild places serve in terms of providing the ecosystem function that agriculture depends upon.

2.5              Whether the threat to UK food security from insect decline receives sufficient cross-government priority.

It does not! However, the threat is much broader and therefore threats to biodiversity need to be integrated into wider food security policy. Importantly, much greater positive communication from the agricultural community is needed. Unless the message emerges from parts of that community, concerns about insect decline will continue to be dismissed as howls from fringe activists.

2.6              Additional policy initiatives and solutions needed in the UK and internationally to reduce and reverse the trends in insect decline.

Policy initiatives are needed to address:

• A failure within academia to ensure data collected on invertebrate abundance reaches the relevant recording schemes in a form that can be utilised well into the future. This problem could be averted by grant-awarding bodies requiring that data gathered in pursuit of PhD and other research programmes be submitted to the NBN upon completion[13].
• The need for training and employing invertebrate specialists in core biodiversity roles. Understanding invertebrates is critical to wildlife conservation and therefore they should be a core part of curricula for all biodiversity courses.

• Measures to retain groundwater and to ensure that groundwater supplies to wetland sites are safeguarded. This should be a priority, especially within south-east England where insect decline is most acute.
• Safeguarding existing wet sites within river catchments and reversing drainage elsewhere.

• Re-wildling projects need to pay a great deal more attention to microhabitat for invertebrates and project design not on a vertebrate scale. Instead, there needs to be a slogan ‘think invertebrate and help a vertebrate’.
• Greater investment in understanding the implications of drought, enhanced soil moisture deficit and effects on forest humidity in order to gain a better understanding of potential climate-driven insect decline.
• Better engagement between academia and ‘amateur’ invertebrate specialists. Currently, almost all of the competency in invertebrate taxonomy lies in the non-vocational community and a substantial amount of the understanding of the ecology of species and assemblages of concern lies there too. This is a wasted opportunity that might be seized by creating a once-yearly forum with funding to facilitate the ‘amateurs’ attendance (costs can be high and many amateurs are far from wealthy). Note, such a forum should be in the winter months so as to avoid clashes with the very short and important ‘field season’.

2.7              Additional comments

2.7.1              Issues around the accessibility of some parts of scientific literature on UK Insects.

Researchers wanting to read published studies relevant to their research, use a limited set of tools to discover publications by other researchers. Prominent among these is Clarivate Analytics Web of Science. If the journal you publish in does not feature in their service, then the chances of other researchers finding your study and citing it are greatly reduced.

The UK has a long and rich history of Natural History enthusiasts and societies, the Dipterists Forum being a relatively recent addition. The Forum publishes a scholarly peer reviewed journal, Dipterists Digest (ISSN 0953-7260) biannually, which covers all aspects of Diptera ecology, behaviour, and conservation, as well as taxonomic acts describing species new to science. As already discussed, the Dipterists Digest does not feature in the Web of Science service.

This issue is not restricted to the literature on UK Diptera, many UK Insect groups have amateur naturalist organisations dedicated to their study and recording (e.g. British Dragonfly Society; Bees, Wasps & Ants recording Society). Many have publications, even if they are not fully formed peer review journals. Together these literature sources represent a huge cache of knowledge on UK insect behaviour and ecology that is largely untapped by the wider research community at present. 

Happily, web-based initiatives such as the Biodiversity Heritage Library (BHL) have proved highly effective at serving to the internet published research from sources that were previously difficult to access. An injection of cash into the UK node for the BHL could see the back-catalogues of UK Natural History journals like the Dipterists Digest digitised, properly indexed, and served to the web in a fully discoverable fashion.

28 April 2023